1. Field of the Invention
The invention relates to a bar code reading device. Such a reading device for a bar code provided in or on a carrier includes a scanning device for line-wise scanning the bar code, a decision element connected to the scanning device to form a bivalent signal from the signal of the scanning device, a code regenerator connected to the decision element to form a code sequence consisting of valid bar widths from the lengths of successive intervals of the bivalent signal, a bar counter counted to an output of the code regenerator in order to count the number of valid bars, and an output element connected to the code regenerator to validate a code sequence and to present a validated code on a user output. Bar codes can be distinguished on the basis of their contents. The first type of code identifies a type of product, for example products sold in supermarkets. The second type of code identifies a product, for example the sequnce number within a number of products of the same type.
2. Description of the Prior Art
A bar code reading device is known from European Patent Application No. 36951 and the corresponding U.S. Pat. No. 4,323,771. The code may be printed on a carrier, but may also be provided in a carrier by punching, etching, etc. The known device utilizes a line scanning camera, for example a Fairchild Model CCD 1410. The lengths of the intervals are compared with two thresholds for the detection of narrow, wide and impossibly wide (out-of-range and hence invalid) bars. However, it has been found that various invalid bars are still accepted. Furthermore, the threshold is adjusted first, and a detection scan can be performed only after that.